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长期的海底天然地震观测由于技术上的困难而极富挑战性.为了在这一领域积累经验,同时揭示南海中央海盆残留洋脊下的岩石圈结构,在南海深海区进行了一次较大规模的被动源海底地震仪(OBS)台阵观测实验.本文简述了此次实验的仪器、OBS的布放和回收状况,着重从多个角度分析了所收集的海底地震记录的数据质量.地震波形分析表明回收的OBS记录质量良好,来自远震、区域性地震和马尼拉俯冲带内的小震的主要震相都清晰可辨.海底背景噪音频谱分析显示OBS记录的噪音水平要高于全球平均噪音模型,且水平和垂直分量的数据质量存在差异,反映了洋流对于OBS各分量的不同影响及各分量与海底的耦合状况;在5~10 s周期范围内,多个OBS台站存在着一个噪音低值区,且水平分量和垂直分量在此频段噪音水平很接近.这一特征与开放大洋的噪音特征不同,说明南海这一边缘海的双频微噪音(double frequency microseism,DFM)的能量来源并不是远源.还利用瑞雷面波的偏振方向规律确定了OBS台站水平分量的方位,并对典型地震的瑞雷面波进行了频散分析.此外,还总结了这一实验对于在南海进行长期的海底天然地震观测的经验和教训.
Long-term natural seismological observation of the seabed is extremely challenging due to technical difficulties.In order to accumulate experience in this field and reveal the lithospheric structure beneath the residual ridge in the central South China Sea Basin, a large-scale Passive Seabed Seismograph (OBS) array observation experiment.This paper briefly described the instrument, OBS deployment and recovery status of the experiment, focusing on the data quality of collected seabed seismic records from many angles.Seismic waveform The analysis showed that the recovered OBS records were of good quality and the major phases of the minor earthquakes from the teleseismic, regional earthquakes and Manila subduction zone are clearly discernible. The spectral analysis of the background noise at the sea floor shows that the noise level recorded by OBS is higher than the global average noise Model and the data quality of horizontal and vertical components are different, which reflects the different influences of ocean currents on the components of OBS and the coupling between each component and seafloor. In the period of 5 ~ 10 s, there is a noise at multiple OBS stations Low value area, and the horizontal component and the vertical component are close to the noise level in this band, which is different from that of the open ocean The energy source of double frequency microseism (DFM) in the sea is not a far source, and the orientation of the horizontal component of OBS station is determined by the law of polarization of Rayleigh surface waves. The Rayleigh surface waves In addition, we also summarize the experience and lessons from this experiment for the long-term observation of the natural seabed in the South China Sea.